No one can give you this advice.
there are two parts to care provided by any care agency
-the agency management and structure
-the actual carers
as to the first part, you need to look at the CQC rating for the agencies in your area. A national chain might have a brilliant branch in Scunthorpe but shit in Skegness.
https://www.cqc.org.uk/
as to the second part, this is why you won't get any sensible advice from strangers on the internet - the single most important aspect of care is the training, standards and personality of the person (or persons as you'll normally have at least two) providing the actual care. This varies enormously within any agency because it's an understaffed and underpaid sector so has high turn over - there will be a lot of workers who are barely trained, just started, don't want to be doing it - when what you need is highly trained, experienced and love it.
Jo who posts on here might use Agency X in Town Y. Her carers from Agency X are Anne and Liz who are brilliant she loves them and tells you Agency X is the bees knees.
Sarah might also use Agency X in Town Y. The carers they send her are Janet and John who are both hating the job and want to leave. She tells you Agency X is the pits.
They are both having different experiences because the staff they get are different.
Word of mouth is helpful but ultimately it's about finding actual staff that are good with the person who needs the care and care needs vary hugely.